The concept of employing spaced-apart apertured discs constructed of electrical insulator material within the quartz tube structure of a metal halide laser is illustrated in U.S. Pat. No. 3,934,22l, entitled "Metal Halide Vapor Laser," issued Jan. 20, 1976, assigned to the assignee of the present invention and incorporated herein by reference. While the concept is illustrated in the above-identified U.S. patent, the concept is not patentable subject matter as to the issued patent.
The use of metal halide to provide substantially reduced operating temperatures in metal vapor lasers has been established with copper halides, lead halides and manganese halides. This concept is disclosed in detail in the above-referenced U.S. patent. With double-pulsed operation in copper halide, for instance, the laser output occurs during the second current pulse with a predetermined pulse separation establishing the maximum operating conditions. Typically, the first pulse dissociates the metal halide to provide sufficient metal atoms in the ground state for electrical excitation into the upper laser levels. Operating the laser at finite repetition rates, each electric current pulse not only excites the existing metal vapor but also continues to dissociate additional metal halide molecules so that the subsequent pulse at a predetermined delay will result in laser emission.
The electrical dissociation of metal halide is a much faster process than is recombination, which proceeds at basically thermal rates. Thus at high repetition rates the metal will precipitate on the walls of the laser tube structure if the period between consecutive pulses is shorter than the recombination time under equilibrium conditions. Metal deposited onto the wall of the laser tube structure not only depletes the lasing material but also leads to a pronounced reduction in the laser tube operating life. A metallic film on the wall functions as a short circuit to the electrical discharge, thereby causing the electrical discharge to move along the wall and eventually overheat and melt the laser tube structure.
While the prior art, such as that represented by U.S. Pat. Nos. 3,522,551 and 3,516,012, discloses the use of metallic apertured discs in laser tube structures, the prior art fails to disclose the operational advantages realized through the use of apertured insulator discs sealed within the quartz tube structure of a metal halide laser.
U.S. Pat. No. 3,522,551 discloses the use of apertured graphite confinement rings positioned within but intermittently spaced from the walls of a laser tube structure. The confinement rings of U.S. Pat. No. 3,522,551 are spaced from the walls for thermal radiation purposes. The apertured graphite confinement rings serve to constrict the plasma to a path corresponding to the aligned apertures of the graphite discs.
The argon laser disclosure of U.S. Pat. No. 3,516,012 employs a quartz tube within which are positioned spaced-apart aperture discs which cooperate with a magnetic field producing means to collimate the laser discharge. Insulators are employed between adjacent apertured discs.